Igniter tube for a propellant charge

ABSTRACT

An igniter tube consisting of a combustible tube, on the inner face of which an ignition charge is deposited along the length of said combustible tube. The invention also relates to a method for producing the igniter tube.

FIELD OF THE INVENTION

The technical field of the invention is that of igniter tubes for propellant charges, having a (cylindrical) central channel.

PRIOR ART

The propellant charges fitted to shells and missiles are ignited by means of a squib combined with an igniter tube. The igniter tube is formed of a combustible tube containing an ignition charge in the form of tablets and/or blocks disposed in the channel of the combustible tube; these tablets or blocks are removable and do not adhere to the combustible tube. The igniter tube thus constituted is placed in the channel of the propellant charge.

The composition of the ignition powder is most frequently gunpowder (GP) consisting of a mixture of potassium nitrate (saltpetre), charcoal and sulfur. There are also other compositions of ignition powder, in particular of the type: Boron/KNO₃, generally in ratio of 70:30 (wt %), a metal (for example iron, aluminium, zinc), a perchlorate-type (for example potassium perchlorate) or fluorinated-polymer-type (for example PTFE (Teflon®) or Viton®) oxidant. The ignition charges (tablets and/or block(s)) described in the prior art consist of an agglomerated ignition powder, optionally with a cellulose binder. In this last case, the ignition charge is obtained by mixing the constituents of the ignition powder with a collodion (solvent+binder), followed by evaporation of the solvent of the collodion. The ignition charge usually called benite is gunpowder agglomerated with a nitrocellulose binder.

Patent application FR-A-2 593 905 describes an ignition charge disposed in a combustible tube consisting of a pile of tablets of agglomerated ignition powder. These assemblies for an igniter tube require both the manufacture of agglomerated powder tablets, as well as their placing in the combustible tube.

It is therefore understood that the ignition charge, placed in the combustible tube, is made of a pyrotechnic material based on an agglomerated powder.

In order that the combustible tube (with a lower combustion rate than the ignition charge) does not screen the combustion gases from the ignition powder, combustible caps are distributed along the length of said tube. These combustible caps, around ten microns thick, rupture with the increase in pressure in the tube generated by the combustion of the ignition charge. Hence, the hot gases developed by the ignition powder can reach, from the onset of the ignition, the parts of the propellant charge located in the vicinity of the openings resulting from the rupture of the caps.

The powder-tablet-based ignition charges of the prior art (familiar to a person skilled in the art) have several disadvantages (that said person skilled in the art does not ignore).

Firstly, the operation of filling the combustible tube with the ignition charge is a delicate operation, in terms of both the handling technique and the pyrotechnic risk (the ignition powder is classified in risk division 1.1 in the sense of the UN GHS classification ((UN) Globally Harmonised System for classification and labelling of chemical products). This operation requires special tooling in order to be automated. Moreover, when the ignition charge is introduced into the tube in admixture with a collodion in order to obtain tablets (in situ), the evaporation time for the solvent of the collodion is long because of the confinement of the collodion loaded in the tube.

Then, the combustible tube has a length equivalent to that of the propellant charge channel, but the ignition charge occupies a volume in relation with its mass. The mass of the charge can vary according to the ignition specifications and/or the nature of the powder. The volume of the ignition charge specified for the ignition can be less than that of the propellant charge channel. The ignition of the propellant charge is therefore not always homogeneous in the tube and thus synchronous along the length of the channel.

This deviates from the ideal conditions of almost instantaneous ignition of the entire (internal) surface of the propellant charge.

Finally, it is sometimes necessary to dismantle the igniter tube of a propellant charge, for example when scrapping or neutralising ammunition. This dismantling of the igniter tube involves an extraction of the ignition charge arranged in the combustible tube. This extraction by direct contact with the agglomerated powder generates a pyrotechnic danger.

Patent application FR-A-2 725 781 proposes replacing the agglomerated powder tablets by an ignition material comprising an ignition composition in powdered form (typically gunpowder) deposited on a flexible support sheet, which is then advantageously rolled up on itself in order to be inserted in a combustible tube to form an igniter tube. In order that the powder (which is just placed on the flexible support) does not fall to the bottom of the igniter tube, the powdered composition must be covered with another flexible sheet (called screen sheet), at least one of the screen and support sheets being coated with adhesive.

This method makes it possible to better distribute the powder charge in the channel of the munition and facilitates the dismantling of the ignition material compared with agglomerated powder ignition material. The ignition material described in patent application FR-A-2 725 781 thus proposes a technical solution to the problems posed by powder-tablet-based ignition materials.

Nevertheless, its implementation is complex because of the handling of the explosive ignition powder classified in risk division 1.1, the control of the regularity of the quantities of powder deposited in piles on the flexible sheet and the geometries of the piles, and the step of covering the piles of powder deposited on the flexible sheet by the sticky screen sheet. To the best knowledge of the applicant, the method described has not been developed and industrialised since the publication of the application in 1994.

In terms of used materials, the flexible sheet and the screen sheet are made of paper, nitrated paper, fabric, plastic or aluminium. These materials do not significantly contribute to the energy input of the ignition charge. The spatial distribution of the ignition energy of the charge is obtained uniquely by the distribution and the volume of the piles of powder.

It is not envisaged to vary the composition of the ignition material in order to optimise the spatial distribution of the energy of the ignition charge. The configuration possibilities in terms of the energy level and spatial distribution of the pyrotechnic objects of patent application FR-A-2 725 781 are therefore limited and controlled uniquely by the mass and spatial distribution of the piles of powdered powder.

It would therefore be useful to be able to have an ignition charge capable of being produced in a simple manner on the industrial scale and enabling a large modularity of the level and spatial distribution of the ignition energy. The present invention proposes to respond to these specifications.

SUMMARY OF THE INVENTION

The present invention relates to a propellant charge igniter tube with (cylindrical) central channel, a method for preparing said igniter tube and a propellant charge comprising the igniter tube. The igniter tube comprises a combustible tube, on the inner face of which an ignition charge is deposited.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents a first alternative of the method for depositing an ignition charge inside a combustible tube.

FIG. 2 represents a second alternative of the method for depositing an ignition charge inside a combustible tube.

FIG. 3A illustrates the circular deposit, with triangular cross-section, of an ignition charge in a combustible tube.

FIG. 3B illustrates the linear deposit, with triangular cross-section, of an ignition charge in a combustible tube.

FIG. 3C illustrates the helical deposit, with triangular cross-section, of an ignition charge in a combustible tube.

FIG. 4 represents an ignition charge in the form of a helical pattern disposed in a combustible tube.

FIG. 5 illustrates a combustible tube provided, on its inner face, with an ignition charge in the form of a helical ribbon.

DESCRIPTION OF THE INVENTION

The present invention relates, according to a first aspect, to a propellant charge igniter tube with (cylindrical) central channel, said igniter tube comprising (consisting of) a combustible tube, made of a combustible material (having the appearance of a felt), comprising a cellulose ester, preferably nitrocellulose, on the inner face of which is deposited and adheres an ignition charge.

The ignition charge is deposited (in adherent manner) on the inner face of the combustible tube, in the form of geometric patterns spaced apart along the length of said tube. The ignition charge contains, as main constituent, at least one ignition powder agglomerated with a cellulose binder (the patterns do not all necessarily contain the same powder). It is obtained by drying a collodion loaded with an ignition powder deposited on the inner face of the tube.

In order to ensure a facilitated insertion and extraction of the combustible tube within the propellant charge (during dismantling, for example), the ignition charge opportunely does not cover the axial ends of the inner face of the tube, which thus leaves a free height for gripping the tube without contact with the ignition charge.

Conventionally, the tube receives, at each of its ends, a cover (commonly called a paillet) serving as a plug. The covers (plugs) are made of a combustible material, generally identical to that of the tube.

The combustible materials constituting the combustible tube and the ignition charge must be chemically compatible and have the property of adhering to one another. For this purpose, they have a common base of cellulose ester, such as cellulose nitrate, cellulose acetate or nitrocellulose. Nitrocellulose is the preferred common base and is selected, in a non-limiting manner, in the rest of the description.

In one embodiment, the combustible tube, such as those marketed by the company Eurenco, consists of 60 wt % to 80 wt % cellulose ester, 17 wt % to 37 wt % cellulose, 3 wt % to 7 wt % resin and 0 wt % to 2 wt % stabilising additive (the sum of these various constituents being equal to 100%). Its mass is about 15 g to 25 g. The combustible tube has a height of about 120 mm to 140 mm, for an inner diameter of 25 mm to 30 mm and a thickness of 1.5 to 2.5 mm.

Advantageously, the combustible tube has the composition given in table 1 and the dimensions given below.

TABLE 1 Composition wt % Nitrocellulose powder cotton 69 Cellulose 25 Resin 5 Stabilising additive 1

The mass of the combustible tube is 18 g+/−3 g. The tube has a height of 126 mm, for an inner diameter of 28 mm and a thickness of 1.8 mm.

In one embodiment, the ignition charge is obtained by drying a collodion (solvent+binder) loaded with an ignition powder. The ignition powder is a conventional ignition powder used for propellant charge ignition. The ignition powder is a powdered granular material classified in risk division 1.1 within the meaning of the UN GHS classification ((UN) Globally Harmonised System for classification and labelling of chemical products). The grains of the ignition powder comprise an inorganic oxidant compound such as KNO₃ or KClO₄, and typically consist of such an inorganic oxidant compound and a reducing compound forming an agglomerated mixture. These rapid combustion and high combustion heat ignition powders are therefore not cellulose materials, such as a dried composite material based on nitrocellulose and nitroglycerin. Examples of ignition powder compositions are given in table 2 below.

TABLE 2 Ignition powder: constituents Chemical formulas Boron/potassium nitrate B/KNO₃ Aluminium/potassium perchlorate Al/KClO₄ Magnesium/Teflon ®-Viton ® Mg/PTFE-TV Zirconium/barium chromate Zr/BaCrO₄ Aluminium/copper oxide Al/CuO Gunpowder S/charcoal/KNO₃ Magnesium/sodium nitrate/potassium nitrate Mg/NaNO₃/KNO₃ Zirconium/lead chromate Zr/PbCrO₄ Zirconium-nickel/potassium ZrNi/KClO₄—Ba(NO₃)₂ perchlorate-barium nitrate Caesium decahydroborate/potassium nitrate Cs₂B₁₀H₁₀/KNO₃

The powder used is preferably gunpowder (GP) having a composition by weight:

-   -   potassium nitrate (saltpetre): ˜75%     -   charcoal: ˜15%     -   sulfur: ˜10%.

Gunpowder (GP) is conventionally classified according to an index relating to its particle size (see table 3, below).

TABLE 3 Residue ≤3% Residue ≥95% Index In the sieve In the strainer In the sieve In the strainer GP1 7.10 mm 10.00 mm 4.00 mm 5.00 mm GP2 4.50 mm  5.75 mm 2.50 mm 3.00 mm GP3 2.80 mm  3.20 mm 1.00 mm 1.40 mm GP4 1.25 mm   1.6 mm 0.71 mm 1.00 mm GP5 1.00 mm  1.25 mm 0.63 mm 0.80 mm GP6 0.80 mm  1.00 mm 0.45 mm 0.50 mm GP7 0.50 mm  0.60 mm 0.10 mm 0.10 mm

Powders with a fine particle size, of the type GP5, GP6 or GP7, are the most suitable in the context of the invention. A fine particle size ensures a better dispersion effect of the powder in the collodion.

The collodion used in the context of the invention is of the type cellulose ester base+solvent(s). In one embodiment, the cellulose ester base of the collodion consists of a cellulose ester (for about 70 wt % to about 90 wt %) and generally contains, in addition, conventionally, at least one plasticiser (about 1 wt % to about 20 wt %, preferably about 10 wt %) and at least one stabiliser of the cellulose ester (about 0.5 wt % to about 5 wt %). It also generally contains at least one additive (>0 wt % to about 1 wt %), for example selected from among anti-adhesion agents, anti-flash agents and antioxidants. It can contain a residual quantity of solvent(s), in particular phlegmatising solvent(s) or (and) solvent(s) for dissolving the cellulose ester used during its manufacture.

Advantageously, the cellulose ester used as a majority component is selected from cellulose nitrate, cellulose acetate and nitrocellulose, the latter being preferred. The weight content of nitrogen of the nitrocellulose is ideally 10.5% to 13.5%, an example being grade E nitrocellulose with a weight content of nitrogen of 11.8% to 12.3%, advantageously equal to 12%.

The plasticiser used to prepare the collodion can be, in particular, a ketone (such as camphor), a vinyl ether (such as LUTONAL® A50 marketed by the company BASF), a polyurethane (such as NEP-PLAST 2001 marketed by the company Hagedorn-NC), an adipate (such as dioctyl adipate) or a citrate (such as triethyl 2-acetylcitrate).

The stabiliser used to prepare the collodion can be, in particular, a compound the chemical formula of which comprises aromatic rings (ideally two aromatic rings), capable of fixing the nitrogen oxides from decomposition of nitric esters (presently nitrocellulose).

Examples of stabilisers may include 2-nitrodiphenylamine (2NDPA), 1,3-diethyl-1,3-diphenyl urea (centralite I), 1,3-dimethyl-1,3-diphenyl urea (centralite II), and 1-methyl-3-ethyl-1,3-diphenyl urea (centralite III).

The optional additive used for preparing the collodion can be selected, in particular, from anti-adhesion agents, such as silicone-type anti-adhesion agents, anti-flash agents, antioxidants, dyes, surfactants, anti-agglomeration agents and hydrophobic agents.

The solvent can be a double solvent of the acetone/butyl acetate (BA) type at 50 wt %/50 wt %.

The collodion is advantageously formulated to lead to a dry extract (after evaporation of the solvent) of 10 wt % to 40 wt %.

Table 4 below presents a formulation of the collodion with 14 wt % dry extract.

TABLE 4 Collodion Composition (wt %) Cellulose ester base Nitrocellulose 84 14 Plasticiser 10 Stabiliser 3.5 Others (additive(s), 2.5 water, solvent, etc.) Total 100 BA 43 Acetone 43 Total 100

In one embodiment, the collodion loaded with ignition powder(s) comprises about 50 wt % to about 70 wt % powder(s), and the rest to 100% (in other words about 30 wt % to about 50 wt %) collodion. Conventionally, the previously constituted ignition powder(s), is (are) added to the collodion.

The collodion loaded with ignition powder is advantageously obtained by addition of the previously constituted ignition powder, in the solvent. It is then given the name “Benite B”. It differs from those of the prior art, designated “benite”, obtained by separate additions to the collodion of constituents of the ignition powder and without plasticiser.

Table 5 below gives an example of a composition of the collodion of table 4, loaded with ignition powder GP7.

TABLE 5 Raw materials Weight (g) Composition (wt %) GP7 10.36 56 Collodion 8.14 44 Total 18.5 100

The collodion loaded with ignition powder is classified in risk division 1.4 within the meaning of the UN GHS (UN Globally Harmonised System for classification and labelling of chemical products). The danger zones to take into account for handling the loaded collodion are therefore reduced, which facilitates the operations of depositing the collodion on the tube.

After drying (evaporation of the solvent) the loaded collodion, the (dry) ignition charge adheres to the inner surface of the combustible tube and comprises about 88 wt % to about 92 wt % ignition powder(s), about 7 wt % to about 10 wt % cellulose ester, the rest to 100% being provided by at least one compound chosen from a plasticiser, an additive and a residual solvent. By way of indication, the dry ignition charge obtained after drying (evaporation of the solvent) of the collodion of table 5 contains the weight ratios indicated in table 6 below.

TABLE 6 Dry Benite B composition Weight (g) wt % GP7 10.36 90.08 Nitrocellulose 0.96 8.35 Plasticiser 0.11 0.96 Stabiliser 0.04 0.35 Residues (water, solvent . . . ) 0.03 0.26 Total 11.50 100.00

According to a second aspect, the present invention relates to a method for preparing an igniter tube by (direct) deposition, by extrusion, of the collodion loaded with ignition powder on the inner face of a combustible tube.

In one embodiment, the surface of the tube intended to receive the deposit can, if necessary, be prepared by sanding prior to the deposit of collodion. Such a step can promote the adherence of the paste on the tube when deposited.

In one embodiment, the deposition of the collodion inside the tube is carried out by means of a telescopic rod 1 fitted at its end with at least one nozzle 3. The collodion is temperature-conditioned in a tank. The collodion passes through a die of predetermined dimensions. The routing of the collodion into the die is carried out by applying a pressure. This pressure determines the flow rate. The die is extended by the rod provided with one or more extrusion nozzles. A plurality of extrusion nozzles is optionally used on the same manufacturing tool, in order to be able to successively or simultaneously combine a plurality of formulations within a given charge. The one or more nozzles can carry out a plurality of passages over a given deposition zone 2 in order to superimpose layers and to increase the local thickness and thus the weight of the ignition charge. According to a first alternative (FIG. 1 ), the tube is stationary and the deposits of collodion on the inner face of the tube are carried out by moving the nozzle. According to a second alternative (see FIG. 2 ), the tube is mounted on a tower which can move axially and in rotation, the nozzle then being stationary. The deposition method according to these two alternatives can be easily industrialised. Once the collodion is deposited, it is left to dry (by evaporation of the solvent) in order to obtain an igniter tube wherein the ignition charge adheres to the inner surface of the combustible tube.

The method according to the invention enables any geometry and arrangement of the ignition charge on the inner face of the combustible tube to be envisaged, provided that this leads to the correct ignition of the ignition charge.

Advantageously, the ignition charge is deposited in the form of spaced point patterns, or spaced circular patterns along the length of the tube, or linear patterns along the length of the tube, or one or more helical patterns along the length of the tube. The deposits are not necessarily all identical in size and/or composition and are not necessarily all arranged in a regular manner. The number of deposits, their geometry and their arrangements constituting the ignition charge in the tube are adjustment parameters of the ignition charge.

In one embodiment, each pattern contains a substantially identical quantity of ignition powder(s) (of the order of about 90 wt %). In another embodiment, the patterns deposited on the inner face of the combustible tube do not all contain the same quantity of ignition powder(s), the quantity of ignition powders(s) in each pattern being in the proportions indicated above (about 88 wt % to about 92 wt %).

FIGS. 3A, 3B and 3C illustrate various geometries of the above-mentioned patterns (circular pattern, linear pattern, helical pattern), said patterns advantageously having a triangular cross-section. An ignition charge in the form of one or more helical patterns is particularly advantageous in terms of ease of deposition and distribution of the charge in the tube.

As indicated below, in an illustrative (and in no way limiting) manner, for an equivalent of a total ignition charge volume of about 10 g in a solid block (prior art), the preferred geometry consists of a helical pattern of an ignition charge deposited in a tube of inner diameter 2.8 cm and length 12.6 cm according to the invention (see FIG. 4 ).

Helical diameter of the pattern: d=2.8 cm

Axial length of the pattern: h=10 cm

Pitch of the helix:=2 cm

Number of turns n=5

Length of the pattern=45.1 cm

Geometry of the cross-section of the pattern: semi-circular

Base length of the cross-section=0.6 cm

Radius of the cross-section: 0.3 cm

Cross-section area of the pattern: 0.14 cm²

Volume of the pattern: 0.14×45.1=6.3 cm³

Density ˜1.6 g/cm³

Weight of the pattern ˜10 g.

Deposition tests of the collodion loaded with ignition powder were carried out on the inner face of a tube (see FIG. 5 ) by means of a device such as described in FIG. 2 . The collodion was dried at room temperature for about 2.5 hours (this duration can be greatly reduced by drying under a flow of hot air, for example at about 80° C.). During this drying, the assembly (tube+ignition charge) could be manipulated. After drying, the deposit had a mass of about 10 g. It was regular along a helical pattern of 10 cylindrical turns of about 0.3 mm diameter, and adhered perfectly to the inner surface of the tube.

According to a third aspect, the present invention concerns a propellant charge comprising an igniter tube as defined above.

The present invention has the advantage that, whatever its weight, the ignition charge can be distributed regularly over the inner face of the combustible tube (this ensures a homogeneous ignition in the tube). 

1. An igniter tube with a central channel consisting of a combustible tube, made of a combustible material comprising a cellulose ester, on the inner face of which an ignition charge is deposited in the form of geometric patterns spaced apart along the length of said combustible tube, and adheres to said combustible tube, said ignition charge comprising 88 wt % to 92 wt % of ignition powder(s) and 7 wt % to 10 wt % cellulose ester.
 2. The igniter tube according to claim 1, wherein the ignition charge further comprises at least one compound chosen from a plasticiser, an additive and a residual solvent.
 3. The igniter tube according to claim 1, wherein the ignition powder is a powdered granular material comprising an inorganic oxidant compound.
 4. The igniter tube according to claim 1, wherein the ignition powder is gunpowder.
 5. The igniter tube according to claim 1, wherein the cellulose ester of the ignition charge is nitrocellulose.
 6. The igniter tube according to claim 1, wherein the combustible tube comprises 60 wt % to 80 wt % cellulose ester, 17 wt % to 37 wt % cellulose, 3 wt % to 7 wt % resin and 0 wt % to 2 wt % stabilising additive.
 7. The igniter tube according to claim 1, wherein the ignition charge is deposited on the inner face of the combustible tube and along the length thereof, in the form of circular patterns.
 8. The igniter tube according to claim 1, wherein the ignition charge is deposited, on the inner face of the combustible tube and along the length thereof, in the form of linear patterns.
 9. The igniter tube according to claim 1, wherein the ignition charge is deposited, on the inner face of the combustible tube and along the length thereof, in the form of helical patterns.
 10. A method for preparing an igniter tube according to claim 1, which comprises depositing by extrusion a collodion loaded with an ignition powder on the inner face of the combustible tube, and drying the deposited collodion, said collodion loaded with ignition powder comprising 50 wt % to 70 wt % ignition powder and 30 wt % to 50 wt % collodion.
 11. The method according to claim 10, wherein the collodion comprises 70 wt % to 90 wt % cellulose ester, 1 wt % to 20 wt % of at least one plasticiser, 0.5 wt % to 5 wt % of at least one stabiliser of the cellulose ester and, optionally, up to 1 wt % of at least one additive.
 12. The method according to claim 11, wherein the cellulose ester is nitrocellulose.
 13. A propellant charge comprising an igniter tube according to claim
 1. 